Age_Hardening

Age_Hardening - Precipitation Hardening or Age Hardening...

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Precipitation Hardening or Age Hardening
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Consider an alloy where solid solubility decreases with decreasing temperature. The equilibrium structure is a θ precipitate in a parent α phase T wt. % B A B α α + θ α α α
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On the basis of dispersion hardening we would expect greater strength if we could create more interfacial surfaces. Therefore let’s divide every θ particle and redistribute it – resulting in a Non-equilibrium structure
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We can attain this through a three-step heat treatment Step 1: Solution treatment Heat into the single phase ( α ) region to erase the existing room-temperature structure and redissolve all B-atoms The temperature for this step is above the solvus but below the eutectic Hold to achieve chemical uniformity
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Step 2: Quench Rapidly cool to suppress diffusion (no θ -phase will form!) Resultant is a superstaurated solid solution ( α ’) containing excessive amounts of dissolved B- atoms Step 3: Age A controlled reheat within the 2-phase region (temperature below the solvus) to activate diffusion This produces a Coherent precipitate
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This note was uploaded on 05/20/2008 for the course MET 121 taught by Professor Kohser during the Spring '07 term at Missouri S&T.

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Age_Hardening - Precipitation Hardening or Age Hardening...

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